Field of the Invention.
The present invention relates generally to a system for detecting an occlusion in a fluid line, and more particularly to a system for detecting occlusions in the upstream or container side of a disposable cassette containing a fluid pump thereon, which disposable cassette includes a pressure diaphragm is for installation onto and use with a main pump unit including electronic control circuitry therein for monitoring fluid pressure upstream of the pump, the control circuitry providing an alarm in the event of a container-side occlusion.
In the past there have been two primary techniques which have been used to deliver drugs which may not be orally ingested to a patient. The first such technique is through an injection, or shot, using a syringe and needle which delivers a large dosage at relatively infrequent intervals to the patient. This technique is not always satisfactory, particularly when the drug being administered is potentially lethal, has negative side effects when delivered in a large dosage, or must be delivered more or less continuously to achieve the desired therapeutic effect. This problem results in smaller injections being given at more frequent intervals, a compromise approach not yielding satisfactory results.
Alternatively, the second technique involves administering a continuous flow of medication to the patient, typically through an IV bottle. Medication may also be delivered through an IV system with an injection being made into a complex maze of IV tubes, hoses, and other paraphernalia. With drop counters being used to meter the amount of bulk fluid delivered, many medications still end up being administered in a large dosage through an injection into the IV lines, although the medications may be diluted somewhat by the bulk fluid.
As an alternative to these two techniques of administering medication to a patient, the relatively recent addition of medication infusion pumps has come as a welcome improvement. Medication infusion pumps are utilized to administer drugs to a patient in small, metered doses at frequent intervals or, alternatively, in the case of some devices, at a low but essentially continuous rate. Infusion pump therapy may be electronically controlled to deliver precise, metered doses at exactly determined intervals, thereby providing a beneficial gradual infusion of medication to the patient. In this manner, the infusion pump is able to mimic the natural process whereby chemical balances are maintained more precisely by operating on a continuous time basis.
One of the requirements of a medication infusion system is dictated by the important design consideration of disposability. Since the portion of the device through which medication is pumped must be sterile, in most applications of modern medication infusion equipment some portions of the equipment are used only once and then disposed of, typically at regular intervals such as once daily. It is therefore desirable that the fluid pump portion of the infusion pump device be disposable, with the fluid pump being designed as an attachable cassette which is of inexpensive design, and which is easily installable onto the main pump unit.
It will be perceived that it is desirable to have a simple disposable cassette design to minimize the cost of construction of the cassette, using the minimum number of parts necessary in the design of the cassette. The design of the cassette must be mass producible, and yet result in a uniform cassette which is capable of delivering liquid medication or other therapeutic fluids with a high degree of accuracy. The cassette should include therein more than just a fluid pump; other features which have formerly been included in peripheral devices may be included in the cassette.
It is the primary objective of the present invention to provide an alarm in the event of an occlusion in the fluid path upstream of the pump in the disposable cassette, between the fluid reservoir (container) and the cassette. The occlusion detection system must be integrally contained in the main pump unit/disposable cassette combination, and not an add-on upstream type detector. A container-side occlusion detector must provide a number of advantages and meet a number of requirements necessary to enhance operating safety of the overall system. Specifically, the container-side occlusion detection system of the present invention must respond quickly to container-side occlusions.
Such situations most commonly occur when a roller clamp that is inadvertently left closed after setup or manual use of the disposable fluid pathway. Other causes of container side occlusions include using an infusion set with a non-vented drip chamber on a non-vented bottle, or attempting to deliver from an emptied syringe. Rapid response is required to prevent failure of the pump to deliver medication to the patient, which failure over a prolonged period may have adverse consequences to the patient.
Most infusion systems use a drop sensor placed on the drip chamber to detect container side occlusions. However, such sensors are not practical for use in ambulatory situations because frequent nuisance alarms will occur because the very nature of the system makes it highly vulnerable to erroneous alarms induced by movement or motion of the sensor. Drop sensors are also disliked because they add clutter to the system and are easily broken. In addition, a drop sensor is not applicable for infusions which use a syringe as the drug reservoir. Therefore, the alarm system of the present invention must detect container side occlusions using a construction which does not require a drop sensor, and which allows the use of syringes as a source of fluid to be infused.
The container-side occlusion detection system of the present invention must also minimize the occurrence of nuisance alarms occurring. It must simultaneously accurately and effectively provide an alarm in the event of true occlusions. The system of the present invention must also allow flexibility in allowing fluids having widely differing fluid viscosities to be used, since some infusates require more pressure to pump than others.
Perhaps most important is the ability of a container-side occlusion detection system to provide an alarm in a minimal time from the onset of an occlusion. This requirement must remain for all rates at which fluid may be infused, and the system of the present invention must afford a high degree of precision and accuracy under all operating conditions and at all operating flow rates. In addition, the occlusion detection system of the present invention must also require low power to operate, to therefore conserve power and extend battery life.
The occlusion detection system of the present invention must be of a design which enables it to compete economically with known competing systems. It must accomplish all these objects in a manner which will retain all of the advantages of ease of use, reliability, durability, and safety of operation, without incurring any relative disadvantage. All the advantages of the present invention will result in a superior medication infusion system having a number of advantages making the system a highly desirable alternative to systems presently available.